Evaluation of fracture healing is based on physical and roentgenographic findings. Such evaluation is subjective and possibly misleading. For example, slight motion is difficult to detect and tenderness is difficult to interpret. Abundant callus may give a misleading appearance of greater strength than is actually present. Because the rate of union is variable, knowledge of time since fracture does not allow precise estimation of union in individual cases. Thus, a method for nondestructive evaluation of fracture union is desirable. We are studying the usefulness of measurements of mechanical resonant frequency and driving point mechanical impedance of fractured bones as indices of healing. We are validating these methods by measuring cadaver bone specimens and correlating the measured resonant frequency and mechanical impedance with bone strength. Periodic measurements are being obtained in dogs following tibial osteotomy as well. We are repeatedly measuring bone resonant frequency of approximately 50 patients with tibial fractures. This study will allow empirical validation of the resonant frequency and impedence techniques as well as test the predictive value of these methods for estimating healing rates of individual patients. Such studies may allow accurate determination of the time when immobilization is no longer required.